title: Microparticle drug sequestration provides a parallel pathway in the acquisition of cancer drug resistance.
abstract: Expanding on our previous findings demonstrating that microparticles (MPs) spread cancer multidrug resistance, we now show that MPs sequester drugs, reducing the free drug concentration available to cells. MPs were isolated from drug-sensitive and drug-resistant sub-clones of a human breast adenocarcinoma cell line and from human acute lymphoblastic leukemia cells. MPs were assessed for size, mitochondria, RNA and phospholipid content, P-glycoprotein (P-gp) expression and orientation and ATPase activity relative to drug sequestration capacity. Of the drug classes examined, MPs sequestered the anthracycline class to a significant degree. The degree of sequestration was likely due to the size of MPs and thus the amount of cargo they contain, to which the anthracyclines bind. Moreover, a proportion of the P-gp present on MPs was inside-out in orientation, enabling it to influx drugs rather than its typical efflux function. This was confirmed by surface immunofluorescence and by assessment of drug-stimulated ATPase activity following MP permeabilization. Thus we determined that breast cancer MPs carried a proportion of their P-gp oriented inside-out, providing active sequestration within the microvesicular compartment. These results demonstrate a capacity for MPs to sequester chemotherapeutic drugs, which has a predominantly active sequestration component for MPs derived from drug-resistant cells and a predominantly passive component for MPs derived from drug-sensitive cells. This reduction in available drug concentration has potential to contribute to a parallel pathway and complements that of the intercellular transfer of P-gp. These findings lend further support to the role of MPs in limiting the successful management of cancer.
authors.affiliation: School of Pharmacy, Graduate School of Health, University of Technology, Sydney, NSW 2007, Australia; Vascular Immunology Unit, Discipline of Pathology, Sydney Medical School and Bosch Institute, The University of Sydney, NSW 2006, Australia. Electronic address: jgon7696@uni.sydney.edu.au.
authors.forename: Joyce
authors.initials: J
authors.lastname: Gong
authors.forename: Frederick
authors.initials: F
authors.lastname: Luk
authors.forename: Ritu
authors.initials: R
authors.lastname: Jaiswal
authors.forename: Anthony M
authors.initials: AM
authors.lastname: George
authors.forename: Georges Emile Raymond
authors.initials: GE
authors.lastname: Grau
authors.forename: Mary
authors.initials: M
authors.lastname: Bebawy
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000970:Antineoplastic Agents / Q000378:metabolism / Q000493:pharmacokinetics*; D001682:Biological Availability; D045744:Cell Line, Tumor; D055252:Cell-Derived Microparticles / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D006801:Humans; D008928:Mitochondria / Q000378:metabolism; D010316:Particle Size; D010641:Phenotype; D010743:Phospholipids / Q000378:metabolism; D012313:RNA / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D010743:Phospholipids; D012313:RNA
keywords: Cancer; Drug sequestration; Microparticle; Multidrug resistance; P-glycoprotein